1. Field of the Invention
The present invention relates to an improved method for treating subterranean, unconsolidated formation. In one aspect it relates to an improved method for preconditioning the wellbore prior to consolidating the formation with synthetic resins.
2. Description of the Prior Art
Difficulties due to solids entrained in produced fluids have led to sand control methods which employ a variety of different synthetic resins for the consolidation of incompetent subterranean formations. These methods involve the injection of a liquid resin or a resin forming material into the formation and permitting the resin to cure to an infusible state, thereby bonding the formation sand in place. Typically, a solvent is injected as a preflush into the formation to remove resident fluids and precondition the formation to be consolidated.
Often, the consolidation treatment is unsuccessful because of contamination of the resin during injection by fluids contained in the wellbore. These contaminating fluids often exist in the casing rathole (i.e. that portion of the casing below a perforated zone adjacent the unconsolidated formation). Typical contaminating fluids include water-base completion fluids, seawater, and formation brine remaining from a well completion or workover operation.
During sand consolidation treatments, the resin being injected into the formation can displace a considerable amount of aqueous rathole contaminating fluid into the formation. This results in a continuous contamination of the resin during injection, resulting in poor consolidation. Moreover, a significant amount of resin accumulates in the rathole and is wasted.
A prior technique for dealing wth the problem of contaminating fluid in the rathole involves circulating a high density brine into the rathole, resulting in a rathole fluid which the resin will not displace. There are several problems with this method. In order to rapidly and efficiently place the high density brine in the well, a pipe which extends to the bottom of the rathole is necessary so that filling can take place from the bottom upwards. This necessitates the use of a workover rig and increases costs. Another disadvantage is the incompatibility of some consolidating fluids with the dense brine. Further, experience has shown that simply mixing the dense brine for filling the rathole is an error-prone process. Finally, even if a high density brine is located in the rathole, contamination of the resin solution still takes place during injection which can cause failure of the consolidation treatment.